In heap leaching, a leaching solution is applied over a bed of ore in order to separate out of the ore a solution that includes metals present in the ore. The ore in the bed may be mined ore material that is crushed or ground into small chunks before being laid in the heap or may be run-of-mine (ROM) raw ore material that has not been crushed or ground.
Such separation of the solution out of the ore may be assisted by bacteria that require aeration of gas such as oxygen and carbon dioxide for their functioning and lack or absence of such aeration may decrease the bacterial activity resulting in less dissolution of metal out of the ore. Aeration may be necessary not only in bacteria-assisted leaching, but also in chemical-assisted leaching, such as cyanide leaching of gold ores, acid leaching of copper and nickel sulphides and chloride leaching of copper sulphide ores.
Heap leaching may be performed in a bed of ore that is dynamically formed for example on an impervious layer or on top of lower layers of ore material that have already been leached. Placing of the ore in such beds proceeds by depositing it upon a leading side face of the bed thus adding to the dynamic formation of the bed in the lateral side direction.
In some cases aeration gas may be urged into the bed of ore by for example perforated piping in order to increase the presence of gas in the bed and thereby enhance leaching rates in the bed. Such perforated piping is typically laid horizontally at the base of a heap and/or below a layer of ore and as a result may exhibit the following exemplary disadvantages: the ore that is laid above the piping may bear down against the piping and squash it, the gas emitted from such piping may not reach all of the ore that is located above it, and the large amount of gas required for enhancing the rate of leaching may result in such piping being of a relatively large diameter which makes this type of piping expensive and low-efficiency.
U.S. Pat. No. 5,030,279 describes a percolating system for circulating a leaching solution through a stationary ore mass. The percolating system includes a series of tubes that have spaced-apart emitters. The emitters are of the type having a labyrinth flow restricting passage and the tubes are positioned on an upper surface of the ore bed to emit the leaching solution directly into the ore. In the case where multiple layers of ore beds are laid one over the other, the percolation systems of the underlying beds are left intact and can be supplied with injected pressurized air instead of the leaching solution in order to enhance oxidation of the leaching solution being emitted from the percolation system that is laid upon the top bed.
U.S. Pat. No. 7,314,066 describes a bioleaching process that includes an aeration system through which air is added to sulfide heaps. The aeration system includes a plurality of air distribution pipes in the form of corrugated HDPE air pipes that are placed at the base of the heaps. Such air distribution pipes when used buried in a heap may exhibit air hole blocking and this patent describes several embodiments of air distributors that address this problem.